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24. Design Patterns
Architecture
Design Patterns
Design patterns are proven, reusable solutions to commonly occurring software architecture problems. Senior engineers use these to build scalable codebases.
🧱 The Module Pattern
Before ES6 modules existed, developers used closures (IIFEs) to create private variables and expose a public API. This prevents variables from polluting the global scope.
const ShoppingCart = (function() {
// Private Array
let cart = [];
return {
// Public API
addItem: function(item) {
cart.push(item);
},
getItems: function() {
return [...cart];
}
};
})();
ShoppingCart.addItem("Laptop");
console.log(ShoppingCart.getItems());
// console.log(ShoppingCart.cart); // Undefined! It is completely private.
Output[ 'Laptop' ]
🏭 The Factory Pattern
Instead of using classes and the new keyword, a Factory pattern is simply a function that manufactures and returns new objects.
function createUser(name, role) {
return {
name: name,
role: role,
permissions: role === "admin" ? ["read", "write", "delete"] : ["read"]
};
}
const user1 = createUser("Alice", "admin");
const user2 = createUser("Bob", "guest");
console.log(user1.permissions);
console.log(user2.permissions);
Output[ 'read', 'write', 'delete' ]
[ 'read' ]
[ 'read' ]
💍 The Singleton Pattern
Ensures that a class or object has only one instance across the entire application (e.g., a Database connection pool or a global configuration object).
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